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ACTIVE INTEGRATED PHOTONIC DEVICES
IN SINGLE CRYSTAL LiNbO3 MICRO-PLATELETS
AND A HYBRID Si-LiNbO3 PLATFORM
by
Yoo Seung Lee
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(ELECTRICAL ENGINEERING)
August 2011
Copyright 2011 Yoo Seung Lee

This work addresses new ultra fast (over 40 Ghz) electro-optic device platforms and their applications using single crystal LiNbO₃ ultra thin films (~1 micrometer) and Si nano-photonics for compact size photonic integrated circuits, optical networks and optical interconnects. ❧ It is divided into two parts: the fabrication of active electro-optic device platforms and the integrations of active electro-optic devices based on these platforms. In the first part, the new fabrication technologies of single crystal LiNbO₃ films, free standing LiNbO₃ micro-platelets, and hybrid Si-LiNbO₃ device platforms were demonstrated and discussed. The second part of this work discusses simulation and experimental work for electro-optically tunable waveguide, micro-ring resonator modulators, active photonic bandgap crystal slab waveguides, and dual-disc resonator for increasing the sensitivity-bandwidth product. ❧ LiNbO₃ thin films have been integrated on SiO₂/LiNbO₃ by He⁺ ions implantation and direct bonding through careful control of the thermal expansion and stress of the implanted wafer and substrate. After slicing the films, their single crystal property and comparable surface roughness (rms ~6 nm) has been presented by XRD and AFM measurements. ❧ Free standing single crystal LiNbO₃ micro-platelets (mm long and 1 micrometer thick) have been obtained from a z-cut LiNbO₃ wafer by He⁺ ions implantation and thermal treatment. They have been first invented by using a different slicing method. They have been transferred, positioned and bonded to SiO₂/LiNbO₃, SiO₂/Si, and Si-on-insulator (SOI: Si/SiO₂/Si) by direct bonding method with optimum annealing conditions. ❧ Hybrid Si-LiNbO₃ electro-optic tunable ring resonators have been proposed and demonstrated as a path to achieving ultra compact and high speed electro-optic devices. The platelets were transferred and thermally bonded on top of Si resonators that were fabricated in an SOI platform by a 0.18 µm standard CMOS process. For the hybrid micro-ring resonator, a FSR of 16.5 nm, a finesse F of ~1.67×10², a Q-factor of ~1.68×10⁴, and an effective r coefficient of ~1.7 pm/V were achieved for the TE mode. These values are in good agreement with the calculated results. ❧ Photonic crystal structures based on LiNbO₃-on-insulator (LOI) platform have been proposed and discussed for active photonic devices. 3D FDTD method has been used in order to design LiNbO₃ photonic slab more precisely. In the E-Beam lithography, electron doses and sizes of the hole have been varied to fine optimum values. Etching methods with various equipments and recipes have been investigated since they were the most important issue to fabricate the real structure. Further work is to fabricate photonic slab waveguide in a LOI structure. ❧ Hybrid Si-LiNbO₃ active photonic slab have been proposed and discussed in order to employ second order nonlinear effect to the Si photonic slab. Bonding between a LiNbO₃ micro-platelet and a Si photonic slab has been demonstrated. In order to optimize hybrid photonic slab, the dimensions of the Si slab have been carefully designed by using PWE method. For this design, ± 10 % error in the radius of the holes appears acceptable. Further work is to integrate the hybrid Si-LiNbO₃ photonic slab waveguide with coplanar electrodes for EO fast tunable filters and EO modulators. ❧ Resonant free spectral range (FSR) RF-optic modulators using dual disc resonators with 2:1 ratio of the radii of the discs have been proposed and theoretically analyzed to increase the sensitivity-bandwidth product compared to a single resonator modulator. The transmission of the coupled resonator structure is analyzed for various coupling parameters. The sensitivity and modulation bandwidth can be increased by factors of 1.9 and 6.4, respectively, for the different cases. The sensitivity-bandwidth product can be increased up to a factor of 3.3 in one design. For 5% error of the ratio of the radius of each disc, errors of the sensitivity and modulation bandwidth were acceptable.

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ACTIVE INTEGRATED PHOTONIC DEVICES
IN SINGLE CRYSTAL LiNbO3 MICRO-PLATELETS
AND A HYBRID Si-LiNbO3 PLATFORM
by
Yoo Seung Lee
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(ELECTRICAL ENGINEERING)
August 2011
Copyright 2011 Yoo Seung Lee